It has long been known that bacteria play a part in pathogenic dental caries. More recently an abundance of research has implicated bacteria as the causative agents of periodontal disease. Researchers have found a relationship between tooth deposits in periodontal disease. In 1965 a causal relationship was demonstrated between the daily accumulation of dental plaque which causes gingivitis. Others demonstrated in dogs that gingivitis if untreated progresses to periodontitis. Some different organisms are involved in gingivitis than those involved in periodontal disease. However, the organisms are in both cases various strains and types of bacteria.
To date, the art of treating caries, gingival and periodontal diseases is primarily surgical although some advances have been made in the control of disease by chemical means. Historically, the use of a toothbrush with dental floss has been recognized as a prevention and a treatment of the initial carious and gingival lesions. However, once the lesions progress beyond their initial stages surgical intervention is the treatment of choice. In the treatment of caries the lesion is excised using a rotating carbide steel or diamond burr mounted in a high speed handpiece. The cavity preparation is designed to accommodate a silver amalgam, gold or composite type of filling material which simulates the physiologic architecture of the tooth. In the treatment of periodontal diseases the goal of treatment is to remove tooth deposits with hand scalers and currettes and to surgically excise the periodontal pocket so the pocket is unavailable to foster growth of microorganisms.
Significant advances have been made in the field of preventative cariology through the employment of fluoride containing dentifrices and through the use of viscous polymers which are painted into the pits and fissures of the crown to obliterate these niches where routine oral hygiene practices are ineffective. The purpose of using fluoride as a nutritional supplement or as a topical agent is to incorporate fluoride into the hydroxyappetite crystalline structure of the enamel. This makes for a more symmetrical and perfect crystal structure which is more resistant to acid demineralization.
Plastic polymeric materials have been shown to be effective in preventing caries by painting them into pits and fissures soon after the eruption of each tooth into the oral cavity. This system works by etching the enamel surface with an acid to leech out surface enamel crystals and make a porous enamel surface. The viscous polymeric materials are painted onto the porous enamel surface and form an intimate mechanical bond with the enamel. Disadvantages of the polymer system include the necessary application of the material immediately after the eruption of the tooth, their propensity to dissolve and abraid and the cost of application.
The control of gingival and periodontal diseases via chemical means has had less success; although, many compounds both in literature and the patent have been proposed for inclusion in dentifrices or mouthwashes. At the present time several chemicals are being considered for their efficacy in preventing or treating periodontal diseases, but there is no accepted therapeutic which is universally recommended by the dental profession. Among such compounds considered for use are quartenary ammonium salts, ceramide peroxide, chlorhexidine, systemic and topical antibiotics, alexidine and other compounds having bactericidal efficacy. This approach recognizes that killing plaque bacteria controls caries, gingival and periodontal diseases.
The bactericidal properties of hydrogen peroxide are due to its dissociation into hydroxyl radicals which are toxic to bacteria. This property led long ago to consideration for its use in an oral dentifrice (U.S. Pat. No. 959,605, U.S. Pat. No. 975,814). However, The peroxide containing dentifrices of the prior art were not universally believed effective bactericides. Recent research has led to the proposal that the reason for their ineffectiveness was the slow dissociation of hydrogen peroxide into free radicals when contained in a typical composition. This dissociation is not rapid enough for a sufficient quantity of bactericidal free radicals to be generated during the application of the composition. An enzymatic method of generating hydrogen peroxide in situ (U.S. Pat. Nos. 4,150,113 and 4,178,362) attempted to overcome this problem by directing the formation of hydrogen peroxide to specific areas. However, this system does not appear to have gained widespread acceptance.
Hydrogen peroxide dissociates into free radicals; it is these free radical species which are known to be bacteriocidal. The rate at which free radical species are generated from the uncatalyzed decomposition of hydrogen peroxide determines the bacteriacidal efficacy of the compound. Enzyme catalyzed reactions are known to occur 10.sup.10 to 10.sup.15 times as rapidly as the corresponding non-enzymatic reaction. In accordance with the present invention an enzyme has been selected to catalyze the reduction of hydrogen peroxide for generating free radicals. The free radicals generated in this process are generated at greatly elevated rates relative to the free radicals generated from the non-enzymatic dissociation of peroxide.
Peroxidases are classified as enzymes which act on hydrogen peroxide as an acceptor of electrons. The different types of peroxidases are distinguished by the donor molecules from which they take electrons to donate to hydrogen peroxide. In accordance with the present invention a peroxidase is used to generate free radicals from donor molecules. The donor molecules must be capable of acting as a substrate for the peroxidase in generating such free radicals. The method of the present invention teaches how to control the generation of free radical species and the period of bacteriacidal activity. A bactericide is formed by combining three components, viz., a peroxide, a peroxidase and a source of donor molecules adapted to act as a substrate for the peroxidase. The bactericide will generate free radicals over a limited time period dependent upon the concentration level of each component and in particular the concentration level of the donor molecules and the peroxide since these components determine the duration of the catalyzed enzyme reaction in generating the free radicals. As long as this reaction continues there will be a supply of free radicals.
The concentration of donor molecules in the bactericide is of paramount importance since the donor molecules are transformed in the reaction into the bactericidal agents. The reaction of the donor molecules with the enzyme is the slowest step in the reaction mechanism. Accordingly the rate of generating free radicals and thus the efficiency of the bactericide is controlled by the quantity of donor molecules present. It has also been discovered in accordance with the present invention that a minimum concentration level of donor molecules exists below which the bactericide is ineffective for treating dental disease i.e., the rate of free radical production is too low to be characterized as having any noticeable bactericidal effectiveness. This minimum level for the donor molecules is at least 1.0.times.10.sup.-5 molar which corresponds to 0.0001%. The minimum concentration level for the peroxidase, to achieve noticeable bactericidal effectiveness, is 0.38.times.10.sup.-3 units per ml and for hydrogen peroxide the minimum concentration level, to achieve noticeable bactericidal effectiveness, is 1.33.times.10.sup.-5 molar which corresponds to 0.00003%. In general the preparation used in the treatment of dental disease should have maximum concentration levels of about 0.1 milligram per ml for the enzyme, 1 milligram per ml for phenylalanine and 3% for hydrogen peroxide.